Known electrochemical systems, for example fuel cell systems or electrochemical compressor systems such as electrolyzers, usually comprise a stack of electrochemical cells separated from each other by metallic bipolar plates. Said bipolar plates usually comprise two individual metallic plates that are typically welded to each other and are normally made of thin metal sheets. The bipolar plates, or the individual plates making up the bipolar plates, may serve, for example, to electrically contact the electrodes of the individual electrochemical cells (e.g., fuel cells) and/or to electrically connect adjacent cells (serial connection of the cells).
The bipolar plates, or the individual plates making up the bipolar plates, may comprise a channel structure adapted for supplying the cells with one or more media and/or for removing reaction products. The media may, for example, be fuels (e.g., hydrogen or methanol), reaction gases (e.g., air or oxygen) or coolants. Such a channel structure is usually arranged in an electrochemically active region (gas distribution structure/flowfield). Furthermore, the bipolar plates, or the individual plates making up the bipolar plates, may be adapted for passing on waste heat generated during conversion of electrical or chemical energy in the electrochemical cell and for sealing the individual media or coolant channels from each other and/or from the outside. The aforementioned channel structures and/or sealing structures, in particular sealing beads, are usually stamped into the individual plates by means of a stamping tool. Similar structures also exist in separator plates used in humidifiers of electrochemical systems. What is said in the following regarding bipolar plates and their individual plates accordingly also applies to separator plates in humidifiers.
It is known to provide each of the individual plates, or of the bipolar plates, with one or more measuring structures. These are structures formed at or on the plates that are detectable by an optical sensor and are used, by utilizing a pattern or image recognition software, to establish a coordinate system oriented in a defined manner relative to the plate. Said coordinate system helps, for example, in measuring the plate, in automatically positioning the plate in a tool, or in measuring structures stamped into the plate or applied to the plate. The tool in which the plate is positionable in a defined manner by means of the measuring structures may be, for example, a joining tool, a coating device, or a cutting device, in particular a die cutting or laser cutting device. Multiple process steps may be performed in a defined position by virtue of measuring relatively to such a measuring structure, e.g., positioning of the laser welding seams, positioning of screen printing for partial coating, etc.
A measuring structure according to this kind is known, for example, from the document DE 102012002053A1, termed a measuring feature (Messmerkmal) there. In a particular embodiment, the measuring feature according to DE 102012002053A1 is a basically circular cavity arranged in an elevated section on the plate. Such rounded cavities can be easily localized, and their center points determined, with known optical measuring systems.
An optical measuring system for localizing said measuring structure comprises, for example, a light source for illuminating the measuring structure and an image detector for capturing an image of the plate with the measuring structure arranged on the plate, wherein the light source and the camera are arranged on the same side of the plate (reflected-light method). The accuracy with which the measuring structures are localizable when the images are captured using the reflected-light method, however, may be impaired to a high degree by the lighting conditions, by the optical properties of the material of the plate surface, or by the optical properties of a coating on the plate surface and/or by the geometrical characteristics of the plate surface.
Transmitted-light methods are more robust methods for localizing measuring structures. With transmitted-light methods, the measuring structure comprises at least one through-hole, and the light source and the image detector are arranged on different sides of the plate so that the light emitted by the light source typically passes through the through-hole orthogonally to the main plane of the plate and is detected by the image detector on the opposite side of the plate. In the transmitted-light method, the image of the measuring structure thus can normally be captured with improved contrast as compared to the reflected-light method. However, in order to form measuring structures having a through-hole, to date the through-hole has to be punched in an additional manufacturing step. On the other hand, if the through-hole is punched during the stamping process, additional punching waste is created in the stamping tool. The punching slugs produced in the process may permanently damage the stamping tools.
If a measuring structure is formed in a process step other than the one in which the remaining stamped structures are formed, an offset may occur between these two types of structure that impedes a reliable positioning or even makes it impossible.
It is thus the object of the present invention to create a metallic plate having at least one measuring structure which plate is suitable for being used in an electrochemical system, the plate being manufacturable in as simple and cost-effective a manner as possible and permitting localization of the measuring structure in as simple a way as possible and with as high an accuracy as possible, particularly relative to the other structures of the plate.